With the continuous development of the display technology, the size of the display is ever-changing. In order to achieve portability of the electronic device, the demand on display screens having a small size is growing.
Meanwhile, the user also needs a display screen having a high display quality. For example, users prefer a high PPI (Pixel per Inch) display screen with improved display accuracy and consistency.
OLED (Organic Light-Emitting Diode) displays have been used more and more widely in a variety of portable electronic devices, since it has light, thin, low power consumption and other preferred characteristics.
The OLED display generally includes an organic light emitting diode array (i.e., a pixel array), driving circuits (i.e., pixel circuits) providing a driving current to the organic light emitting diodes in the array, and a scanning circuit providing a driving signal to the pixel circuits.
However, in the conventional OLED display, the pixel circuit usually compensates only for the threshold voltage (Vth) of the driving transistor, without considering the degradation of the carrier mobility in the driving transistor, that of the light emitting element and other issues caused by the accumulated service time. For example, as the time passes, when a current flows through the light emitting element, the forward voltage drop of the light emitting element (the minimum forward voltage at which the light emitting element can be turned on with a predetermined forward current) increases. The light emitting element is usually connected to the source/drain of the driving transistor, so that the potential difference between the source and the drain of the driving transistor decreases. Therefore, the light emitting current flowing through the light emitting element decreases. Since there are a plurality of light emitting elements and driving transistors in the OLED display, and the degradation of the respective light emitting elements and the change of the carrier mobility of the driving transistors are various, the display luminance of these light emitting elements is also various, even if an identical display signal is provided to each of the pixel circuits, and the display uniformity of the OLED display is further compromised.